1. Field of the Invention
The present invention relates to an image pickup device in which a group of focus detection pixels for detecting a focus based on a phase difference are discretely arranged in an image pickup pixel group, and an image pickup apparatus including the image pickup device.
2. Description of the Related Art
In recent years, image pickup devices in which focus detection pixels that receive and photoelectrically convert light fluxes resulting from pupil division are discretely arranged in an image pickup pixel array, i.e., image pickup devices that perform what is called image plane phase difference AF, have been put into practical use and commercialized. A phase difference occurs between the light fluxes resulting from the pupil division according to displacements from a focal position, and the focus detection pixels are intended to detect the phase difference.
The focus detection pixels are arranged at a certain ratio relative to image pickup pixels, and the arrangement ratio is a relatively large ratio, for example, a ratio of one pixel out of eight pixels. Also, the arrangement range of focus detection pixels arranged in image pickup devices are changing from an arrangement range that is only a particular partial region of the pixel section to an arrangement range that is a larger region (for example, the entire pixel section), that is, the arrangement range tends to enlarge. Thus, the total number of focus detection pixels included in the image pickup devices amounts to some large number.
For readout of the focus detection pixels, there are several schemes that can be employed according to, e.g., the readout frequency (readout rate), the instantaneousness and/or the readout method, and it is preferable to optimize readout efficiency for each readout scheme.
For example, Japanese Patent Application Laid-Open Publication No. 2010-181751 describes an image pickup apparatus that performs image plane phase difference AF, the image pickup apparatus being configured to select a plurality of thinned readout modes. The image pickup apparatus includes: an image pickup device that includes a group of first pixels that generate first signals for image generation and a group of second pixels that generate second signals for phase difference detection by dividing a pupil region of a taking lens; a focus adjustment section that adjusts a focus of the taking lens based on the signals from the group of second pixels; a readout section having a first thinned readout mode in which signals from a plurality of pixels are thinned out at a predetermined thinning ratio and a thinning phase and then read out, and a second thinned readout mode in which signals from a plurality of pixels are thinned out at a thinning ratio and a thinning phase, at least either of the thinning ratio and the thinning phase being different from that of the first thinned readout mode, and read out; and a selection section that selects either of the first thinned readout mode and the second thinned readout mode for operation of the image pickup apparatus, according to the state of the image pickup apparatus. It is then described that in an image pickup apparatus including an image pickup device in which focus detection pixels are discretely arranged, image quality deterioration attributable to focus detection pixels is suppressed when pixel signals are read out from the image pickup device in a thinned-out manner.
Column parallel-type AD converters are proposed as a configuration for reducing an AD conversion processing time period in image pickup apparatuses, and examples thereof include an image pickup apparatus described in Japanese Patent Application Laid-Open Publication No. 2013-051497. In the image pickup apparatus, a reference signal having a first gain, and a reference signal having a second gain that is different from the first gain, which are reference signals for converting levels of analog pixel signals obtained from pixels to digital data, are generated at the time of pixel data level readout, the levels of the analog pixel signals and the reference signals are compared with each other, counting processing is performed in parallel with the comparison processing, a first count value at a point of time when the processing for comparison with the reference signal having the first gain is obtained as digital data, and if the first count value does not reach a predetermined threshold value, a second count value at a point of time when the processing for comparison with the reference signal having the second gain is obtained as digital data.
As the basic configurations of the image pickup apparatuses, currently, CMOS-type solid image pickup apparatuses using CMOS (complementary metal oxide semiconductor) transistors prevail, and general CMOS-type solid image pickup apparatuses employ a scheme in which signal charges generated by photoelectric conversion sections in respective pixels arrayed in a two-dimensional matrix are sequentially read out on a row-by-row basis. In this scheme, timings for exposure in the photoelectric conversion sections in the respective pixels are determined by a start and an end of signal charge readout, and thus, the exposure timings are different for the respective rows. Therefore, a simultaneous image pickup function (global shutter function) that provides signal charge accumulation simultaneity. This global shutter function is preferable also from the perspective of phase difference detection accuracy enhancement, and examples thereof include Japanese Patent Application Laid-Open Publication No. 2013-009294.